SEATTLE — A year ago, when rowdy demonstrators swarmed through the city streets on May Day, smashing storefront windows and swarming police, downtown business owners were outraged. A federal grand jury was convened, and Mayor Mike McGinn ordered a thorough review, vowing to do better.

Wednesday’s May Day demonstration unfolded in banner-waving harmony through much of the late afternoon, as more than 3,000 marchers supporting worker and immigrant rights streamed through downtown.

But a smaller, much rowdier “anti-capitalist/anti-state” march launched later from Capitol Hill. By the end of the night, police were using pepper spray against a streaming crowd that was smashing windows and hurling rocks, bottles, metal rods and fireworks.

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“We’re a bigger and better city than this. I look at this and I am disappointed that this is the picture the world sees of us,” McGinn told reporters.

Police reported 17 arrests, with eight officers injured, mostly from being struck by objects hurled by the crowd.

“The behavior of the group during the evening demonstration steadily escalated into violence,” police said in their report on the evening’s events.

The march began at Seattle Central Community College and the crowd began by breaking windows at several Capitol Hill businesses, including a Walgreen’s. Marchers then made their way down to the city’s retail core, shoving TV reporters and igniting a device that sent a cloud of orange smoke wafting down the block.

A woman driving by was injured by flying glass when a protester hurled a bottle at her car, police said. There was was “limited damage” to structures.

Private security guards and police on bicycles formed barriers around the usual downtown targets such as NikeTown.

The main conflict occurred when officers moved in to make arrests and the rock- and bottle-throwing crowd surged around police and the vehicles in which detainees were placed, police incident commander Chris Fowler told reporters.

Police deployed "blast ball" grenades, which unleashed an explosive but largely harmless cloud of pepper spray that finally moved the crowd of several hundred back toward Capitol Hill.

"That first march came downtown. It was absolutely peaceful ... it was almost a festive affair and they had some serious messages, too, that they wanted to express. No incidents whatsoever," McGinn said at a news conference.

"The second march was very different, and it wasn't just merely because it was unpermitted. I think it also had to do with the nature of the individuals in it and what they wanted to do."

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kim.murphy@latimes.com